1. Technical Field
The present invention relates to a stator vane of a turbo molecular pump and particularly to the reduction of breakage of the stator vane.
2. Background Art
A vacuum pump has, in general, a rotor rotatably installed inside a pump case and by high-speed rotation of this rotor, rotor vanes integrally cut out in a number of stages around the rotor are also rotated at a high speed. On the inner periphery of the pump case, stator vanes and the rotor vanes are alternately arranged in a number of stages.
By interaction of the stator vanes and the rotor vanes arranged alternately in a number of stages, exhaust action of a gas molecule is carried out, and a process chamber or the like of a semiconductor device to which this vacuum pump is connected is brought into a vacuum state. That is, the rotor vane on the uppermost stage rotating at a high speed imparts a downward motion to a gas molecule having entered from a gas inlet, and the gas molecule having the downward motion is guided to the stator vane and fed into the rotor vane on the subsequent stage. By repeated operation of the above imparting of the motion to the gas molecule and feeding it in many stages, the gas molecule on the gas inlet side is sequentially transferred to the inside of a screw stator below a rotor and exhausted, by which the inside of the process chamber or the like of the semiconductor device is made vacuum.
An interval between the stator vane and the rotor vane performing the above exhaust operation of the gas molecule is set extremely small so that the gas molecule can be exhausted efficiently.
The stator vane is arranged radial in plural between an inner rim portion 32 and an outer rim portion 33 as shown in FIG. 7A, for example, and arranged in a vacuum pump as a stator vane B in the integrally connected state. Also, the stator vane B is generally positioned and fixed in many stages alternately with the rotor vane through a spacer on the inner circumference of the pump case by holding the outer rim portion 33.
As mentioned above, the stator vanes B are arranged alternately with the rotor vanes in many stages, and the stator vane shape is a ring and the rotor vanes are integrally cut out in many stages around the rotor. Thus, it is not possible to arrange them in the vacuum pump by placing the center hole portions of the ring-shaped stator vanes B over the rotors. Therefore, this stator vane B needs to be divided before being arranged in the vacuum pump.
For example, this type of stator vane B is in a construction that two stator vane halves 30, provided respectively with an inner rim portion 32, the outer rim portion 33, and a plurality of stator blades 31, 31 arranged radial between the inner rim portion 32 and the outer rim portion 33 as shown in FIG. 7B, are abutted to each other by a method as shown in FIGS. 7A and 7B to have the ring state. And the stator vane halves 30 are inserted respectively from both sides with the rotor between them and arranged in the vacuum pump alternately with the rotor vane by being combined in the ring state in the above method.
When abutting to arrange the two stator vane halves 30 between the rotor vanes, an inner rim end 32a and an outer rim end 33a are to be positioned in the ring shape. Since the rotor vane is integrally cut out as mentioned above and the outer rim portion 33 of the stator vane half 30 is positioned and stacked through the spacer, the abutted state of the inner rim end 32a can not be checked from the outside.
That is, when the stator vane half 30 in the semi-ring shape is to be positioned and arranged inside the vacuum pump, the positioning is carried out only by the outer rim end 33a capable of being visually checked from the outside, while the inner rim end 32a is positioned and arranged without visual check in general.
This stator vane half 30 in the same semi-ring shape is manufactured in plural from the viewpoint of cost reduction, work efficiency and the like using a punching press or the like (Patent Document 1).
Therefore, when the two stator vane halves 30 are abutted to each other as in FIG. 7A, the inner rim end 32 and the outer rim end 33a of each of the stator vane half 30 should be also abutted to each other and positioned on an abutment line L. However, there is a variation in manufactured stator vane half 30 and the inner rim end 32a might be formed longer in the circumferential direction than a design dimension with respect to the abutment line L at the punching press.
If one or two of such defectively manufactured stator vane halves 30 are abutted as above and positioned/arranged in the vacuum pump, since the abutted state of the inner rim ends 32a cannot be checked, the inner rim ends 32a might collide with each other and overlap each other or be warped as shown in FIGS. 9A and 9B, which leads to the following problem.
That is, the interval between the stator blade 31 and the rotor vane is set extremely small as mentioned above. Thus, if the overlap or warping as shown in FIGS. 9A and 9B occurs in the inner rim end 32a, the interval is further narrowed, and the overlapping or warped portion might contact the rotor vane and result in breakage of the stator blade 31 in the end.
Prevention of a cause of such breakage of the stator blade 31 is particularly important in terms of ensuring of safety and avoidance of danger, but with such a construction as described in Patent Document 2 that the stator vane B formed by abutting the two stator vane halves 30, that is, a construction of the fixed vane B formed by abutting the two stator vane halves 30 manufactured so that the inner rim ends 32a and the outer rim ends 33a are located on the abutment line L, the breakage in the stator blade 31 caused by the overlap or warping of the inner rim end 32a can not be prevented and as a result, the breakage in the stator blade 31 can not be reduced.
Patent Document 1: Japanese Patent Laid-Open No. 2003-269365
Patent Document 2: Japanese Patent Laid-Open No. 5-157090
The present invention was made in order to solve the above problem and has an object to provide a stator vane of a turbo molecular pump suitable for reduction of breakage in a stator vane.